The present embodiments relate to a method and an apparatus for verifying an irradiation field.
Radiation therapy is an established method, in which ionizing radiation is used to treat pathological tissue (e.g., tumor tissue). The aim of radiation therapy is to irradiate the tissue to be treated with an adequate therapeutic dose and in the process, simultaneously protect the healthy surrounding tissue. The therapeutic effect is based, for example, on tumor cells generally having a poorer ability to repair for DNA damage on account of ionizing radiation than cells of healthy tissue.
Image guided radiation therapy (IGRT) enables uncertainties in the irradiation of the target volume to be reduced. IGRT allows visualization of the target volume, organs at risk (OAR) and healthy surrounding tissue prior to the start of an irradiation in order to open up the possibility of irradiating the target volume more precisely.
In order to be able to better determine patient changes between the fractions, a computed tomography recording (also CT for computed tomography) may be produced on the same couch prior to each irradiation. The position of the tumor may therefore be readjusted.
In order to observe the patient movement during the irradiation, the MV therapy beam may also be used for projection imaging (e.g., “portal imaging”). Systems also exist that, in addition to the MV therapy beam, also have a further x-ray source and an additional x-ray sensitive detector. Aside from projective monitoring of the patient movement, CT imaging may therefore also be operated as a movement control.
Sectional views are used to create irradiation plans for radiation therapy. The sectional views represent the region to be irradiated in a three-dimensional manner. CT images are predominantly used.
A light source may be used in radio oncology for a visual check of an irradiation field. The light source is collimated by the multi level collimator (MLC). The field thus projected is made congruent or in alignment with patient markers using patient couch movements. If congruence is achieved, the irradiation field is verified visually.
In the emitter head of the medical linear accelerator (LINAC), a light source is projected into the radiation path via a mirror. The adjustment of the light source and also of the mirror is very time-consuming and is regularly controlled by the user. A useful installation height along the radiation axis is provided on account of the mirror that may be moved to and fro into the radiation path.